Semiconducting organic molecules, metal oxides, conjugated polymers, and other presently unconventional electronic materials are being developed for use in electronic devices. By taking advantage of the special optical properties of such materials, novel optoelectronic devices can be fabricated within the classes of photoconductors and chemical sensors.
Materials such as organic molecules typically possess lower mobilities than inorganic semiconductors, due to the weak interactions between neighboring molecules (van der Waals forces). Creating useful electronic devices using these low-mobility materials is further complicated by the inherent coupling between the optical and electrical properties of the materials. Typically, strong absorbers act as insulating materials, and weak absorbers are conductive. Separation of the optical and electrical functions of the device into separate layers (and thus incorporating heterojunctions) to take advantage of each material's strength can improve device performance.
Photovoltaic devices can produce electrical current in response to excitation of an active component of the device. Excitation can be stimulated by illuminating the device with an appropriate wavelength of light. One class of photovoltaic devices, thin film photovoltaics, employs thin amorphous semiconducting layers to absorb light and generate charge carriers. Often, two types of semiconductors with dissimilar energy level structures are paired together to form a heterojunction where charge can be separated.